It is well-known in transmission control systems to use automatic devices to control shift shock or smoothness of fluid actuated powershift clutches. One well-known form of such devices are referred to as trimmers which have been used as in-line trimmers wherein the oncoming engagement rates of several powershift clutches are controlled by one trimmer or as individual clutch trimmers wherein the oncoming engagement rate of each powershift clutch is controlled by a different trimmer. In-line trimmers in control systems have the advantage of size, simplicity, and cost since only one trimmer is used. However, in-line trimmers have a disadvantage in that every shift is accomplished with the same oncoming engagement rate or clutch pressure rise characteristic which prohibits programming each clutch according to its own needs. Individual clutch trimmers overcome the disadvantage but of course do so with the disadvantage of increased size, reduced simplicity, and increased cost.
Further, when either in-line or individual trimmers are used in control systems for preselect transmissions, wherein a single powershift clutch is used to complete shifts into a plurality of ratios, both type of trimmers are less than satisfactory since every shift or engagement of that clutch is accomplished with the same pressure rise characteristic.